The present invention relates to a level sensor for detecting the level of a liquid or a powder or particulate accumulation (hereinafter referred to as a powder or particulate level).
One example of this type of level sensor is shown in FIG. 35. This sensor includes a pipe member 90 having a plurality of vertically disposed proximity switches 90a, and a float 91 surrounding pipe member 90 and having a magnet 91a on its inner peripheral side.
The magnet 91a moves up and down with the float in response to the rise and fall of the liquid surface. In this level sensor, the level of liquid can be determined by sensing which proximity switch 90a the magnet 91a is next to.
The following problems exist in this known level sensor:
(1) Since sensing is possible only when the float 91 comes to a certain position where one of the proximity switches 90a is present, the liquid level can be determined only up to certain discrete values.
(2) Since the float 91 moves up and down with respect to the pipe member 90, dust and the like can become clogged between the float 91 and the pipe member 90, thereby inhibiting the smooth response of the float 91, and resulting in failure to detect the level of the liquid. In other words, many mechanical elements end up with poor reliability.
(3) This sensor cannot detect the level of the interface between an upper liquid layer and a lower liquid layer.